Malignant gliomas are the most prevalent type of primary tumors of the central nervous system (CNS). The symptoms of a patient with glioblastoma depend on which part of the central nervous system is affected. A brain glioma can cause headaches, nausea and vomiting, seizures, and cranial nerve disorders as a result of increased intracranial pressure. A glioma of the optic nerve can cause visual loss. Spinal cord gliomas can cause pain, weakness, or numbness in the extremities. Gliomas do not metastasize by the bloodstream, but they can spread via the cerebrospinal fluid and cause “drop metastases” to the spinal cord.
High-grade gliomas are highly-vascular tumors and have a tendency to infiltrate. They have extensive areas of necrosis and hypoxia. Often tumor growth causes a breakdown of the blood-brain barrier in the vicinity of the tumor. As a rule, high-grade gliomas almost always grow back even after surgical excision.
Gliomas can not be cured. The prognosis for patients with high-grade gliomas is generally poor, and is especially so for older patients. Of 10,000 Americans diagnosed each year with malignant gliomas, only half are alive 1 year after diagnosis, and 25% after two years. Those with anaplastic astrocytoma survive about three years. Glioblastoma multiforme (GBM) has a worse prognosis.
Treatment for brain gliomas depends on the location, the cell type and the grade of malignancy. Often, treatment is a combined approach, using surgery, radiation therapy, and chemotherapy. The radiation therapy is in the form of external beam radiation or the stereotactic approach using radiosurgery. Spinal cord tumors can be treated by surgery and radiation. Temozolomide is a chemotherapeutic drug that is able to cross the blood-brain barrier effectively and is currently being used in therapy.
Glioblastomas are the most common primary CNS malignant glioma in adults, and account for nearly 75% of the cases. Although there has been steady progress in their treatment due to improvements in neuroimaging, microsurgery and radiation, glioblastomas remain incurable. Despite the combination of surgery, radiotherapy, and chemotherapy, the median survival of patients with glioblastoma is limited to approximately one year, and the five-year survival rate following aggressive therapy including gross tumor resection is less than 10%. Glioblastomas cause death due to rapid, aggressive, and infiltrative growth in the brain. Failure of conventional treatments can be attributed to i) the precarious locations of the tumors within the brain, ii) the infiltrative nature of malignant gliomas that prevents the complete resection of all cancer cells, and iii) the lack of specificity of anti-tumor agents for neoplastic tissue that leads to severe neurotoxicity.
Therefore, there is still a need for an efficient anti-tumor drug that is able to treat gliomas, e.g. glioblastomas, without triggering neurotoxicity.
Among antitumor drugs, antimitotic agents represent an important class. Drugs, such as the taxane family, promote excessive stability of microtubules. In contrast, the Vinca alkaloids induce depolymerization of microtubules. By suppressing microtubule dynamics or functions, such drugs lead to the disruption of mitotic spindle function, the arrest of cell cycle progression, and eventually apoptosis (Mollinedo et al., 2003).
WO 2005/121172 described recently that small polypeptides, corresponding to the tubulin-binding site (TBS) and located in intermediate filament proteins (namely the neurofilament light chain protein NFL, keratine 8, GFAP, and vimentin) penetrate in tumor cells (e.g. MCF7, T98G, LS187, Cos, or NGP cells) where they disrupt the microtubule network and reduce their viability. More particularly, Bocquet et al (2009) showed that the second tubulin-binding site of the NFL protein (hereafter called “NFL-TBS.40-63”) is able to inhibit the proliferation of neuroblastoma and glioblastoma cell lines in vitro.
However, it was impossible, based on those results, to anticipate the behavior and activity of NFL-TBS.40-63 in vivo, in particular on cell lines derived from malignant glioma.
Actually, it is well known that most of the chemotherapies based on microtubule-targeting drugs fail, for the two following main reasons: first, such drugs often result in the development of drug resistance, mediated by overexpression of transmembrane efflux pumps or the expression of tubulin isotypes and/or mutants that confer resistance (Dumontet et al., 1999). Second, they lack specificity for cancer cells and therefore induce unwanted toxicities (Mollinedo et al., 2003). Consequently, the use of microtubule-interacting agents has not been adapted for treating malignant gliomas that have a less than 20% response rate to conventional chemotherapy (Hofer et Herrmann, 2001) and for which existing treatments are commonly associated with debilitating toxic side effects (Cavaletti et al., 1997). A major challenge in the field of brain tumor was thus to identify an antitumoral agent which demonstrates therapeutic efficiency but a better specificity than the microtubule-targeting agents for brain tumour cells over normal tissue.
In this context, the Inventors have shown for the first time that a microtubule-depolymerizing peptide surprisingly demonstrates a unique specificity in vivo for glioma cells, thereby destroying their microtubule network and inhibiting their proliferation without obviously affecting the viability of the surrounding healthy cells.
The results presented below reveal that, when this peptide is injected by stereotaxy in rats bearing an intracranial F98 glioma, the size of the tumor is reduced by approximately 50%, and the health status of animals is significantly improved. Importantly, immunohistochemical staining revealed the presence of the peptide only in the tumor tissue, even 24 days after its injection, while it rapidly disappeared when injected into the same region of the brain in normal animals.
Together, these results demonstrate a selective uptake of the peptide used in the invention by glioma cells both in cell cultures and in animal models, where it significantly decreases their proliferation. Thus, it represents a promising tubulin-binding candidate for treating malignant gliomas.